What is DNA ?
It is the heredity material in human and DNA full form is deoxyribonucleic acid.it is found in the Cells of all living things.
DNA contains all of the genetic information that makes who you are and every .
It contain phosphorus in the form of phosphate. DNA is well- suited for biological information storage.
DNA is bipolymer consist of nucleotide as monnomeric unit.
DNA is double helical structure in eukeriyote
and prokaryote , but presented as monopartite.
In eukeriyote - DNA is presented in nucleus and it is surrounded by nuclear membrane.
In prokaryote-DNA is presented in nucleoid region of cytoplasm without nuclear ki.
In virus - DNA is presented in core of virus surrounded by protein layer and this layer called to "capsoid".
Location of DNA
DNA is located in the " Cell nucleus "but in small amount of DNA can also be found in the " Mitochondria".
DNA Structure
DNA has three main component
1- Deoxyribose or pantose Suger
2- Base
3- phasphate
1- Deoxyribose - DNA contain Deoxyribose suger or pantose Suger.
2- Base - there are four different base
. it is divided into two parts
. a)- pyrimidines
. b)- purine
a) Pyrimidines- it is made by one- sixth. member of ring.
1)Thymin
. 2) Cytosine
b) purines- it is made by a six member ring . and fused to a five ring .
1) Adenine
2) Guanine
3) Phasphate - it is a form of phasphorus.
Double Helix Model
In 1953, Watson and crick postulated a three dimensional model of DNA structure.
It consist of two helical polynucleotide chains. Two polynucleotide chains coil around the same axis to form a right - handed double helix and it is a antiparallel.
The base pair are 0.34nm apart in DNA helix. A complete turn of helix takes 3.4 nm, therefore in each helical turn, 10 bases are present. The external diameter of helix is 2nm.
A suger and phasphate "backbone" connects nucleotides in a chain .
The helix has external grooves, the narrow groove is called at Minor groove.while a wide groove is called at Major groove.
Major groove is the site of dna binding proteins.
Minor groove is the site for small binding molecules .
The pair of bases are always between a purine and pyrimidine, specially the pair
A-T , G-C, which are the base pairs found by chargarff.
There is hydrogen bonding between the bases. 2H bonds between Adenine and thymine and three hydrogen between Guanine and cytosine .
Types of DNA
It has three type DNA -
1) A- DNA
2) B- DNA
3) Z - DNA
1) A- DNA - it is the many possible double helical structure of DNA.
It is most active along with other forms .
A- DNA is similar to B-DNA structure
It has deep major groove and shallow minor groove .it is a right handed but 2.3 nm makes a turn and there are 11 base pairs per turn.
2) B- DNA - it is most DNA and it is conformation in vivo .it is also known as watson and crick model .
It is a narrow, more elongated helix than A.
Wide major groove easily accessible to proteins and narrow minor groove .
Base pairs nearly perpendicular to helix axis one spiral is 3.4 nm .
3) Z- DNA - Z- DNA is the one of the most possible double helical structure of DNA .
Helix has left handed sense and it is most active double helical structure ,12 base pairs found in this DNA .
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